Strain Limits for Concrete Filled Steel Tubes in AASHTO Seismic Provisions

INE/AUTC 13.1

The Effect of Load History on Reinforced Concrete Bridge Column Behavior

INE/AUTC 12.1

Seismic Performance of Steel Pipe Pile to Cap Beam Moment Resisting Connections

INE/AUTC 13.0

A high-resolution model of the external and induced magnetic field at the Earth’s surface in the northern hemisphere

We describe a method of producing high-resolution models of the Earth’s combined external and induced magnetic field (EIMF) using the method of Empirical Orthogonal Functions (EOFs) applied to the SuperMAG archive of ground-based magnetometer data. EOFs partition the variance of a system into independent modes, allowing us to extract the spatiotemporal patterns of greatest dynamical importance without applying the a priori assumptions of other methods (such as spherical harmonic analysis, parameterised averaging, or multi-variate regression). We develop an approach based on that of Beckers and Rixen [2003] and use the EOF modes to infill missing data in a self-consistent manner. Applying our method to a north polar case study spanning February 2001 (chosen for its proximity to solar maximum and good data coverage), we demonstrate that 41.7% and 9.4% of variance is explained by the leading two modes, respectively describing the temporal variations of the Disturbance Polar types 2 and 1 (DP2 and DP1) patterns. A further 14.1% of variance is explained by four modes that describe separate aspects of the motion of the DP1 and DP2 systems. Thus, collectively over 65% of variance is described by the leading 6 modes and is attributable to DP1 and DP2. This attribution is based on inspection of the spatial morphology of the modes, and analysis of the temporal variation of the mode amplitudes with respect to solar wind measures and substorm occurrence. This study is primarily a demonstration of the technique and a prelude to a model spanning the full solar cycle

The Effects of Load History and Design Variables on Performance Limit States of Circular Bridge Columns

This report discusses a research program aimed at defining accurate limit state displacements which relate to specific levels of damage in reinforced concrete bridge columns subjected to seismic hazards. Bridge columns are designed as ductile elements which form plastic hinges to dissipate energy in a seismic event. To satisfy the aims of performance based design, levels of damage which interrupt the serviceability of the structure or require more invasive repair techniques must be related to engineering criteria. For reinforced concrete flexural members such as bridge columns, concrete compressive and steel tensile strain limits are very good indicators of damage. Serviceability limit states such as concrete cover crushing or residual crack widths exceeding 1mm may occur during smaller, more frequent earthquakes. While the serviceability limit states do not pose a safety concern, the hinge regions must be repaired to prevent corrosion of internal reinforcing steel. At higher ductility demands produced by larger less frequent earthquakes, reinforcing bar buckling may lead to permanent elongation in the transverse steel, which diminishes its effectiveness in confining the concrete core. Bar buckling and significant damage to the core concrete represent the damage control limit states, which when exceeded lead to significant repair costs. Furthermore, rupture of previously buckled bars during subsequent cycles of loading leads to rapid strength loss. The life safety or collapse prevention limit state is characterized by fracture of previously buckled bars. The goal of the experimental program is to investigate the impact of load history and other design variables on the relationship between strain and displacement, performance strain limits, and the spread of plasticity. The main variables for the thirty circular bridge column tests included: lateral displacement history, axial load, longitudinal steel content, aspect ratio, and transverse steel detailing. A key feature of the experiments is the high fidelity strain data obtained through the use of an optical 3D position measurement system.Column curvature distributions and fixed-end rotations attributable to strain penetration of reinforcement into the footing were quantified. The following sequence of damage was observed in all of the cyclically loaded experiments: concrete cracking, longitudinal steel yielding, cover concrete crushing, confinement steel yielding, longitudinal bar buckling, and fracture of previously buckled reinforcement. The first significant loss in strength occurred when previously buckled reinforcement fractured. The measured data was used to refine strain limit recommendations. Particular attention was paid to the limit state of longitudinal bar buckling, since it limited the deformation capacity of all of the cyclically loaded specimens. Empirical expression were developed to predict the compressive strain at cover crushing, the compressive strain at spiral yielding, and the peak tensile strain prior to visible buckling after reversal of loading. In design, limit state curvatures are converted to target displacements using an equivalent curvature distribution. The Modified Plastic Hinge Method was developed to improve the accuracy of strain-displacement predictions. Key aspects of the proposed model which differentiate it from the current method include: (1) a decoupling of column flexure and strain penetration deformation components, (2) a linear plastic curvature distribution which emulates the measured curvature profiles, and (3) separate plastic hinge lengths for tensile and compressive strain-displacement predictions. In the experiments, the measured extent of plasticity was found to increase due to the combined effects of moment gradient and tension shift. The proposed tension hinge length was calibrated to match the upper bound of the measured spread of palsticity. The proposed compressive hinge length only contains a term related to the moment gradient effect. Expressions which describe the additional column deformation due to strain penetration of reinforcement into the adjoining member were developed. When compared to the current technique, the Modified Plastic Hinge Method improved the accuracy of both tensile and compressive strain-displacement predictions. Abstract for Volume 3: This report presents the numerical portion of the research project on the impacts of loading history on the behavior of reinforced concrete bridge columns. In well-detailed reinforced concrete structures, reinforcing bar buckling and subsequent bar rupture serve as common failure mechanisms under extreme seismic events. Engineers often use a strain limit state which is associated with bar buckling as the ultimate limit state, but the relationship between the strain demand and resultant bar buckling is not well understood. Past research has indicated large impact of the cyclic loading history on the strain demand to achieve reinforcing bar buckling. On the other hand, sectional analysis is widely implemented by engineers to relate strain to displacement. However, the cyclic load history also has potential impact on the relationship between strain limits and displacement limits. As a result, it is important to study the seismic load history effect on the strain limit state of reinforcing bar buckling and on the relationship between local strain and structural displacement. In addition, Performance-Based Earthquake Engineering (PBEE) strongly depends on an accurate strain limit definition, so a design methodology needs to be developed to identify the strain limit for reinforcing bar buckling including the seismic load history effect. Two independent finite element methods were utilized to accomplish the goal of this research work. First, fiber-based analysis was utilized which employed the Open System for Earthquake Engineering Simulation (OpenSees). The fiber-based method was selected because of its accuracy in predicting strains and its computational efficiency in performing nonlinear time history analysis (NTHA). The uniaxial material models in fiber-based sections were calibrated with data from material tests. In addition, strain data and force-deformation response from large scale testing assists selection of element types and integration schemes to ensure accuracy. The advanced beam-column elements and material models in OpenSees resulted in a very accurate prediction of strain at local sections as well as global dynamic response of structures. A number of nonlinear time history analyses with 40 earthquake ground motions were conducted to investigate the effect of seismic load history on relationship between structural displacement and strain of extreme fiber bars at the critical section. The second finite element model was established with solid elements to predict bar buckling. The model included a segment of reinforcing bar and its surrounding elements, such as spiral turns and concrete. This model separates itself from previous bar buckling research by utilizing actual sectional detailing boundary conditions and plastic material models instead of the simplified bar-spring model. The strain history is considered as the demand on this model. A series of strain histories from the experimental tests and fiber-based analyses were applied to the finite element model to study their impacts on the strain limit for reinforcing bar buckling. Initial analytical investigations have shown significant impact of load history on the strain demand to lead to reinforcing bar buckling in the plastic hinge region. This is also confirmed in the experimental observation which only included a limited number of load histories. The parametric study extended the range of load history types and also studied the effect of reinforcement detailing on bar buckling. On the other hand, analyses with fiber-based models showed that the load history rarely impacts the relationship between local strain and structural displacement. A design approach was developed to include the load history effect on the strain limit state of bar buckling.Volume I: LIST OF TABLES __________________________________________________ xv LIST OF SELECTED NOTATIONS _________________________________ xxxii Chapter 1: Introduction _______________________________________________ 1 1.1 Background – Performance Limit States ______________________ 1 1.2 The Need for Research ___________________________________ 3 1.3 Research Goals and Scope _________________________________ 5 Chapter 2: Test Setup, Instrumentation, Construction, and Text Matrix ______ 6 2.1 Test Setup _____________________________________________ 6 2.2 Test Matrix ____________________________________________ 13 2.3 Instrumentation ________________________________________ 16 2.4 Construction Process ____________________________________ 22 2.4.1 Construction Sequence ______________________________________ 23 2.4.2 Optotrak Target Marker Application Method _____________________ 39 Chapter 3: Experimental Observations _________________________________ 41 3.1 Contents of Report Volume 2 _____________________________ 41 Chapter 4: The Effect of Load History on Column Performance ____________ 43 4.1 Introduction ___________________________________________ 43 4.1.1 Test Setup ________________________________________________ 46 4.1.2 Instrumentation ____________________________________________ 50 4.1.3 Loading Protocol ___________________________________________ 51 4.2 Experimental Results ____________________________________ 55 4.2.1 Damage Observations _______________________________________ 55 4.2.2 Test 11 – Response to the Kobe 1995 Earthquake _________________ 55 4.2.3 The Effect of Load History on Reinforcement Bar Buckling _________ 58 4.3 Spread of Plasticity _____________________________________ 63 4.3.1 Test 16 – Deformation Components Three Cycle Set Load History with #3 Spiral at 1.5” (38mm) _______________________________________ 63 4.3.2 Measured Spread of Plasticity _________________________________ 69 4.4 Conclusions ___________________________________________ 70 Chapter 5: Impact of Steel Content, Aspect Ratio, and Axial Load Ratio on Column Performance ________________________________________________ 72 5.1 Test Setup and Instrumentation ____________________________ 73 5.2 Symmetric Three-Cycle-Set Loading Protocol ________________ 75 5.3 Gradual Bar Buckling Mechanism with Inelastic Transverse Steel Restraint ______________________________________________ 78 5.3.1 North Reinforcement ________________________________________ 79 5.3.2 South Reinforcement ________________________________________ 81 5.4 Transverse Steel Detailing Variable Experiments ______________ 85 5.5 Aspect Ratio Variable Experiments _________________________ 90 5.6 Longitudinal Steel Content Variable Experiments _____________ 92 5.7 Axial Load Ratio Variable Experiments _____________________ 95 5.8 Equivalent Viscous Damping _____________________________ 98 5.9 Conclusions __________________________________________ 102 Chapter 6: Bridge Column Response Prediction Techniques ______________ 104 6.1 Background and Motivation _____________________________ 104 6.1.1 Experimental Program ______________________________________ 104 6.2 Measured Deformation Components _______________________ 107 6.3 Response Prediction Methods ____________________________ 111 6.3.1 Sectional Response Prediction _______________________________ 112 6.3.2 Member Response Prediction ________________________________ 113 6.3.3 Motivation for a New Equivalent Curvature Distribution ___________ 116 Chapter 7: Modified Plastic Hinge Method _____________________________ 118 7.1 Goals for the Modified Plastic Hinge Method ________________ 118 7.2 Deformation due to Strain Penetration of Reinforcement into Adjoining Members ____________________________________ 120 7.3 Tensile and Compressive Plastic Hinge Lengths _____________ 128 7.4 Tensile Strain-Displacement Predictions using the Modified Plastic Hinge Method ________________________________________ 149 7.5 Compressive Strain-Displacement Predictions using the Modified Plastic Hinge Method __________________________________ 152 7.6 Elastic Force-Deformation Predictions using the Modified Plastic Hinge Method ________________________________________ 157 7.7 Conclusion ___________________________________________ 160 Chapter 8: Performance Strain Limits for Circular Bridge Columns _______ 183 8.1 Background __________________________________________ 183 8.2 Experimental Program __________________________________ 186 8.2.1 Loading Protocol __________________________________________ 188 8.3 Observed Damage Sequence _____________________________ 189 8.4 Equation to Predict Peak Tension Strain Prior to Bar Buckling Upon Reversal of Load ______________________________________ 193 8.5 Column Deformation at Peak Tensile Strain Prior to Bar Buckling ____________________________________________________ 197 8.6 Berry (2006) Statistical Drift-Based Bar Buckling Model for Circular Bridge Columns _______________________________________ 200 8.7 Berry (2006) Bar Buckling Model Applied to the Goodnight et al. Dataset ______________________________________________ 202 8.8 Evaluation of Strain Based Bar Buckling Predictions for the Berry (2006) Dataset ________________________________________ 204 8.9 Drift Based Approach Considering Combined Berry (2006) and Goodnight et al. Datasets ________________________________ 208 8.10 Feng (2013) Bar Buckling Strain Limit Expressions from Finite Element Analysis ______________________________________ 211 8.11 Bar Buckling Predictions for the Combined Berry (2006) and Goodnight et al. Dataset ________________________________ 221 8.12 Evaluation for Full Scale Column Experiments by Cheok and Stone (1989) _______________________________________________ 223 8.13 Compressive Strain at Cover Concrete Crushing _____________ 226 8.14 Compressive Strain at Spiral Yielding in Confinement Regions of the Column ______________________________________________ 227 8.15 Residual Crack Widths _________________________________ 232 8.16 Conclusion ___________________________________________ 234 Chapter 9: Design Recommendations for Limit State Displacements ________ 238 9.1 Performance Strain Limits _______________________________ 238 9.1.1 Serviceability Limit States __________________________________ 239 9.1.2 Intermediate Compressive Limit State _________________________ 239 9.1.3 Damage Control Limit States ________________________________ 240 9.2 Modified Plastic Hinge Method ___________________________ 244 9.2.1 Strain Penetration Length and Tension/Comp. Plastic Hinge Lengths _ 248 9.2.2 Elastic Displacements for a Column in Single Bending ____________ 249 9.2.3 Elastic Displacements for a Column in Double Bending ___________ 249 9.2.4 Inelastic Displacements for a Column in Single Bending ___________ 250 9.2.5 Inelastic Displacements for a Column in Double Bending __________ 250 Chapter 10: Future Research on the Effects of Seismic Load Path __________ 251 10.1 Problem Statement _____________________________________ 251 10.2 Background __________________________________________ 251 10.3 Brief Load Path Literature Review ________________________ 260 10.3.1 Yuk-Lung Wong, T. Paulay, and M. J. Nigel Priestley (1993). “Response of Circular Reinforced Concrete Columns to Multi-Directional Seismic Attack” __________________________________________________ 260 10.3.2 E. Osorio, J.M. Bairán, and A.R. Marí (2012). “Effects of Biaxial Shear Loading on the Seismic Response of RC Columns” _______________ 261 10.3.3 Kazuhiro Tsuno and Robert Park (2004). “Experimental Study of Reinforced Concrete Bridge Piers Subjected to Bi-Directional Quasi-Static Loading” ________________________________________________ 263 10.3.4 Stathis N. Bousias, Guido Verzeletti, Michael N. Fardis, Eugenio Gutierrez (1995). “Load Path Effects in Column Biaxial Bending with Axial Force” 266 10.4 Study Objectives ______________________________________ 268 10.5 Research Plan _________________________________________ 268 10.5.1 Task One: Detailed Literature Review _________________________ 268 10.5.2 Task Two: Load Path Analysis _______________________________ 269 10.5.3 Task Three: Experimental Studies on Columns __________________ 269 10.5.4 Task Four: Analysis of Data and Model Calibration _______________ 274 10.5.5 Task Five: Recommendations ________________________________ 274 REFERENCES ____________________________________________________ 275 Volume 2: LIST OF TABLES ___________________________________________________ x LIST OF SELECTED NOTATIONS __________________________________ xiv Chapter 1: Experimental Observations __________________________________ 1 1.1 Load History Variable Tests 8-12 ___________________________ 1 1.1.1 Test 9 – Symmetric Three Cycle Set Load History __________________ 6 1.1.2 Tests 8 and 8b – Chile 2010 Earthquake and Cyclic Aftershock LH ___ 35 1.1.3 Tests 10 and 10b – Chichi Earthquake and Cyclic Aftershock LH _____ 61 1.1.4 Test 11 – Kobe 1995 Earthquake Load History ___________________ 89 1.1.5 Test 12 – Japan 2011 Earthquake Load History __________________ 108 1.2 Load History and Transverse Steel Variable Tests 13-18 _______ 131 1.2.1 Test 13 –Three Cycle Set Load History with #4 Spiral at 2.75” (1.3%) 135 1.2.2 Test 14 –Three Cycle Set Load History with #3 Spiral at 4” (0.5%) __ 160 1.2.3 Test 15 – Three Cycle Set Load History with #3 Spiral at 2.75” (0.7%) 187 1.2.4 Test 16 – Three Cycle Set Load History with #3 Spiral at 1.5” (1.3%) 215 1.2.5 Test 17 – Chile 1985 Earthquake LH with #3 Spiral at 1.5” (1.3%) ___ 241 1.2.6 Test 18 – Darfield NZ 2010 EQ LH with #3 Spiral at 1.5” (1.3%) ____ 274 1.3 Aspect Ratio and Axial Load Variable Tests 19-24 ___________ 304 1.3.1 Test 19 – Aspect Ratio of 5.33 and 10% Axial Load ______________ 308 1.3.2 Test 20 – Aspect Ratio of 5.33 and 5% Axial Load _______________ 336 1.3.3 Test 21 – Aspect Ratio of 7.33 and 5% Axial Load _______________ 365 1.3.4 Test 22 – Aspect Ratio of 7.33 and 10% Axial Load ______________ 395 1.3.5 Test 23 – Aspect Ratio of 8.67 and 5% Axial Load _______________ 425 1.3.6 Test 24 – Aspect Ratio of 8.67 and 10% Axial Load ______________ 455 1.4 Steel Content and Axial Load Variable Tests 25-30 ___________ 488 1.4.1 Test 25 – 24” Dia. Column with 2.1% Long. Steel and 5% Axial Load 492 1.4.2 Test 26 – 24” Dia. Column with 2.1% Long. Steel and 10% Axial Load 525 1.4.3 Test 27 – 24” Dia. Column with 1.6% Long. Steel and 10% Axial Load 561 1.4.4 Test 28 – 18” Dia. Column with 1.7% Long. Steel and 15% Axial Load 598 1.4.5 Test 29 – 18” Dia. Column with 1.7% Long. Steel and 20% Axial Load 635 1.4.6 Test 30 – 18” Dia. Column with 3.1% Long. Steel and 15% Axial Load 671 Chapter 2: Weldability of A706 Reinforcing Steel _______________________ 707 2.1 Test 7 and Weldability of A706 Reinforcing Steel ____________ 707 2.2 A706 Steel Properties and Weldability for Tests 1-6 and 7-12 ___ 712 2.3 Conclusion ___________________________________________ 713 Chapter 3: Summary of Column Tests 1-6 ______________________________ 717 3.1 Test Setup and Instrumentation for Specimens 1-6 ____________ 717 3.2 Test 1: Pushover Load History ___________________________ 720 3.3 Test 2: Three-Cycle-Set with Full Cover Concrete ____________ 722 3.4 Test 3: Three-Cycle-Set with Cover Blockouts _______________ 727 3.5 Test 4: 1940 El Centro Earthquake Load History _____________ 731 3.6 Test 5: 1978 Tabas Earthquake Load History ________________ 737 3.7 Test 6: 1978 Tabas Earthquake Load History ________________ 744 REFERENCES ____________________________________________________ 748 Volume 3: Chapter 1: Introduction ____________________________________________________ 1 1.1 Background and Scope ___________________________________________ 1 1.2 Layout of Report ________________________________________________ 2 Chapter 2: Literature Review _______________________________________________ 3 2.1 General Discussion ______________________________________________ 3 2.2 Relevant Articles on Numerical Simulation ___________________________ 3 2.2.1 Fiber-Based Modeling of Reinforced Concrete Members ____________ 3 2.2.2 Finite Element Method for Reinforcing Bar Buckling _______________ 8 2.3 Chapter Summery _______________________________________________ 9 Chapter 3: Fiber-Based Modeling of Circular Reinforced Concrete Bridge Columns 10 3.1 Introduction and Background _____________________________________ 10 3.2 Theory of Fiber-Based Modeling __________________________________ 12 3.3 Proposed methods for simulating RC bridge columns __________________ 18 3.3.1 Experimental Observation ____________________________________ 18 3.3.2 Proposed Method to Predict Strain Gradient ______________________ 22 3.3.3 Method to Include Strain Penetration ___________________________ 26 3.3.4 Benchmark Method to Capture Nonlinearity in RC Member with Fiber-Based Model 29 3.4 Calibration and Application of the Fiber Model _______________________ 30 3.4.1 Calibration on Material Constitutive Models _____________________ 31 3.4.2 Prediction on Force and Strain from Static Tests __________________ 32 3.4.3 Prediction on Response of Shake Table Tests _____________________ 42 3.5 Chapter Conclusions ____________________________________________ 44 Chapter 4: Load History Effect on Relationship between Strain and Displacement __ 45 4.1 General Discussion _____________________________________________ 45 4.2 Ground

Achilles tendinopathy alters stretch shortening cycle behaviour during a sub-maximal hopping task

Objectives To describe stretch shortening cycle behaviour of the ankle and lower limb in patients with Achilles tendinopathy (AT) and establish differences with healthy volunteers. Design Between-subjects case-controlled. Methods Fifteen patients with AT (mean age 41.2 ± 12.7 years) and 11 healthy volunteers (CON) (mean age 23.2 ± 6.7 years) performed sub-maximal single-limb hopping on a custom built sledge-jump system. Using 3D motion analysis and surface EMG, temporal kinematic (lower limb stiffness, ankle angle at 80 ms pre-contact, ankle angle at contact, peak ankle angle, ankle stretch amplitude) and EMG measures (onset, offset and peak times relative to contact) were captured. Data between AT and CON were compared statistically using a linear mixed model. Results Patients with AT exhibited significantly increased lower limb stiffness when compared to healthy volunteers (p \u3c 0.001) and their hopping range was shifted towards a more dorsiflexed position (p \u3c 0.001). Furthermore, ankle stretch amplitude was greater in AT compared with healthy volunteers (p \u3c 0.001). A delay in muscle activity was also observed; soleus onset (p \u3c 0.001), tibialis anterior peak (p = 0.026) and tibialis anterior offset (p \u3c 0.001) were all delayed in AT compared with CON. Conclusions These findings indicate that patients with AT exhibit altered stretch-shortening cycle behaviour during sub-maximal hopping when compared with healthy volunteers. Patients with AT hop with greater lower limb stiffness, in a greater degree of ankle dorsiflexion and have a greater stretch amplitude. Likewise, delayed muscle activity is evident. These findings have implications in terms of informing the understanding of the pathoaetiology and management of AT

High-speed AFM with a light touch

No abstract available

Coupled Mg/Ca and clumped isotope analyses of foraminifera provide consistent water temperatures

The reliable determination of past seawater temperature is fundamental to paleoclimate studies. We test the robustness of two paleotemperature proxies by combining Mg/Ca and clumped isotopes (Δ47) on the same specimens of core top planktonic foraminifera. The strength of this approach is that Mg/Ca and Δ47 are measured on the same specimens of foraminifera, thereby providing two independent estimates of temperature. This replication constitutes a rigorous test of individual methods with the advantage that the same approach can be applied to fossil specimens. Aliquots for Mg/Ca and clumped analyses are treated in the same manner following a modified cleaning procedure of foraminifera for trace element and isotopic analyses. We analysed eight species of planktonic foraminifera from coretop samples over a wide range of temperatures from 2 to 29°C. We provide a new clumped isotope temperature calibrations using subaqueous cave carbonates, which is consistent with recent studies. Tandem Mg/Ca–Δ47 results follow an exponential curve as predicted by temperature calibration equations. Observed deviations from the predicted Mg/Ca-Δ47 relationship are attributed to the effects of Fe-Mn oxide coatings, contamination, or dissolution of foraminiferal tests. This coupled approach provides a high degree of confidence in temperature estimates when Mg/Ca and Δ47 yield concordant results, and can be used to infer the past δ18O of seawater (δ18Osw) for paleoclimate studies

923-3 Fluosol Reduces Myocardial Reperfusion Injury by Prolonged Suppression of Neutrophils by its Detergent Component (RheothRx) and not by Enhancing O2Delivery

Fluosol, a complex mixture of O2carrying perfluorocarbons (PFCs) emulsified by the detergent pluronic F-68 and a variety of lipids, significantly reduces myocardial reperfusion injury (RI) in animals and humans as shown in some initial clinical trials. Potential mechanisms for Fluosol include enhanced O2delivery to the reperfused tissue and modulation of various neutrophil (PMNs) functions. Recent studies in dogs and man demonstrate the same beneficial effect for treatment of Rl with the detergent component alone, RheothRx, which is currently undergoing clinical trials. We have shown that the effect of Fluosol on PMNs is related to this detergent. However, prolonged infusion (48 hrs) of detergent is required to reduce Rl to the same extent as Fluosol given over only 1 hr. Possible mechanisms for the beneficial effects of Fluosol (O2delivery vs effects on PMNs) were investigated in a model of regional ischemia utilizing rabbits undergoing 30mins of circumflex occlusion and 48 hrs of reperfusion. Infarct size (area of necrosis, AN) was determined histologically and expressed as percent of risk region (area at risk, AR). Animals received Fluosol (30cc/kg) with or without O2or saline over the first 60mins of reperfusion. AR was similar in all groups. (Mean±SEM of AN/AR (%), n=11 for all groups). The treatment with Fluosol with or without O2(44±3 and 40;±3, respectively) was significantly (p<0.05) reduced compared to control (63±4). Another group received F-I08, a larger size pluronic detergent found to be 2.5-fold more potent in suppressing PMN function in vitrocompared to F-68, during the first 3 hrs of reperfusion. This treatment did not alter the infarct size (63±5). RheothRx was found to form 4 nm micelles in solution whereas Fluosol formed particles approximately 100 times larger. Similar sized particles were formed by substituting the perfluorocarbons with mineral oil. The in vitroactivity of this pluronic/mineral oil micelle on PMN function was similar to Fluosol. Infusion of these larger oil micelles was tolerated by rabbits and used in further infarct studies.ConclusionsThese studies suggest that (1) reduction of RI by Fluosol is not due to enhanced O2delivery by the PFCs to reperfused myocardium and (2) since the Fluosol emulsion markedly reduces the clearance of the detergent F-68 (t½: Fluosol ≅ 8 hrs vs RheothRx ≅ 1.5 hrs). prolonged PMN suppression rather than potency of suppression is the mechanism whereby Fluosol ameliorates RI. Fluosol's clinical efficacy may be enhanced by prolonging its infusion to ensure an adequate blood level to suppress PMN function beyond the time of reperfusion injury. RheothRx's clinical usefulness may be facilitated by decreasing its renal clearance by delivering larger micelles of the detergent in order to produce prolonged PMN suppression with a shorter infusion time